Biomedical Engineering Reference
In-Depth Information
An alternative process developed by Frens produces 40-nm gold particles.
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Fol-
lowing this procedure, 50 mL of HAuCl
4
(0.01% solution w/v) is put to boil
before adding 0.5 mL of 1% solution of trisodium citrate. Upon addition, the
solution has a gray color which changes to lavender and with continued boiling
for 1-3 min, develops wine-red color. Further heating or addition of citrate solu-
tion does not change particle diameter after the colloid is formed. A change in the
proportions of components results in an increase of some 20% in the final par-
ticle size. Another process is found in a protocol published by McFarland et al.
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Purification to remove all components with a maximized recovery of the
synthesized AuNP from solution involves centrifugation at different forces
(3000, 5000, 7000, 9000, and 11,000
g
) and five durations (10 min, 20 min,
30 min, 45 min, and 60 min) by following a purification process that involves
centrifugation and washing.
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After centrifugation, the AuNP pellets are imme-
diately resuspended in ultrapure water. The process can be repeated to remove
all other undesirable components and to harvest stable AuNPs. The size of the
resulting AuNPs can be controlled through the percentage of the citrate used in
solution.
2.2.2 Citrate AuNP Characterization
Similar to the chemical analysis and elemental quantification of QDs, AuNPs
can be analyzed using inductively coupled plasma mass spectrometry (ICP-MS)
(Perkin Elmer, Massachusetts, USA). ICP-MS quantification is done by direct
injection of samples into the ICP-MS sample holder. The presence of non-
AuNP components (chloride, citrate, ketoglutarate, and acetate) in the synthe-
sized AuNP solution can be examined with ion chromatography (IC) system
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after passing a 1-5 mL sample of the AuNP solution through a nylon syringe
filter (pore size: 0.45 mm) to remove AuNPs. Removal of the AuNPs is impor-
tant to ensure that IC columns were protected from possible interference from
the AuNPs. To monitor losses and instrument performance in the process, an
internal standard (oxalate, 32.8 mg) needs to be spiked to the synthesized AuNP
solution
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to monitor procedural loss and instrument performance in a tripli-
cate analysis. The total organic carbon (TOC) present in the reactant solution
(HAuCl
4
and citrate) and in the product (synthesized AuNP) solution can be
established using a TOC analyzer. Aggregation of the AuNPs can be established
with a Zeta Trac Analyzer to assess stability over time and storage temperature.
2.2.3 AuNP Characterization with X-Ray Photoelectron
Spectroscopy
To establish the AuNPs oxidation state, an X-ray photoelectron spectroscopy
(XPS) coupled with a Kratos AXIS His spectrometer (Kratos Analytical Ltd,
UK) is suggested. Preparation of sample is summarized below as previously
described.
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